Many different devices and systems use amplifiers for amplifying various signals. For precision applications, amplifiers with low offset, low noise, a well-defined gain, and a clean continuous output signal are often desired or required. Traditionally, amplifiers with trimmed bipolar input stages have been used, but these types of input stages typically draw bias currents from signal sources due to base currents of the bipolar transistors.
To obtain true high-impedance inputs, metal oxide semiconductor (MOS) input stages can be used, but these types of input stages are typically associated with much higher offset and 1/f noise than their bipolar counterparts. Dynamic offset cancellation (DOC) techniques can be used to mitigate these disadvantages. Two common approaches for dynamic offset cancellation are chopping and auto-zeroing. However, chopped amplifiers typically produce spurious signals at their outputs, while auto-zeroed amplifiers typically have increased low-frequency noise.